1. Field of the Disclosure
This disclosure relates to an electric power control device for a hybrid electric power system, and particularly, to an electric power control device for a hybrid electric power system, capable of improving quality of output electric power in a hybrid electric power system including at least two types of electric power generators.
2. Background of the Disclosure
In recent years, electric power consumption keeps increasing around the world. However, an increase in electric power generating facilities is getting difficult due to limitation on the construction of large thermal electric power stations and nuclear power stations due to problems obtaining land sites, environmental issues, resource supply and demand and the like. Also, the sophistication of the overall industry leads to an increase in demands on electric power quality. Accordingly, requirements for developing various types of energy sources that take into account demand, management and control are increasing.
Responsive to this tendency, a hybrid electric power system using renewable energy, such as wind power, solar power, fuel cell energy and the like, is being developed. The hybrid electric power system diversifies electric power supply sources for supplying electric power and allows for selection of electric power supply sources according to conditions of the electric power system, so as to improve energy efficiency, reverse transmission of electric power, and reliability. Such hybrid electric power system is emerging as a next generation electric power Intelligent Technology (abbreviated as IT).
FIG. 1 is a block diagram illustrating a general hybrid electric power system.
As illustrated in FIG. 1, a general hybrid electric power system 10 may be connected to a main grid 20. The hybrid electric power system 10 may distribute electric power in such a manner of selecting and adjusting electric power supplied from at least two renewable energy supply sources according to a change in a quantity of electric power required by an electric load (abbreviated as load hereinafter) 30.
The general hybrid electric power system 10 may maintain electric power supplied to the load 30 by appropriately distributing electric power supplied from the main grid 20 and at least two types of renewable energy supplied.
In more detail, the electric power supplied from the main grid 20 may be delivered to the load 30 through a transformer via a common connection point with the hybrid electric power system 10.
The general hybrid electric power system 10 may include renewable energy generators, for example, a solar energy generator (Photovoltaic generator, abbreviated as PV hereinafter) and a fuel cell energy generator(abbreviated as FC hereinafter), which are linked to each other by a DC link, so as to supply electric power through an DC/AC converter. A PWM control device of a DC/DC converter connected to the PV may efficiently control an output of the PV by a maximum electric power point tracking technology. Also, a PWM control device of a DC/DC converter connected to the FC may control a voltage of the DC link to control changes in outputs of the fuel cell in response to the change of the load 30.
FIG. 2 is a view illustrating changes in output electric power of the general hybrid electric power system 10.
As illustrated in FIG. 2, under a state that an output of the PV is constant, an output of the FC may be required in response to the change of the load 30.
However, as illustrated in the graph of FIG. 2, in spite of a drastic change in a quantity of load-required electric power, an output response of the fuel cell energy generator FC is not fast. Consequently, an entire amount of output electric power (PV+FC) may gradually increase and then gradually decrease in spite of the drastic change in the quantity of load-required electric power.
The delay of the output response rate may cause a problem involved with electric power quality. Especially, when a load shedding or the like occurs in the electric power system, the output of the FC may be continuously maintained for a predetermined time, which may cause instability and an erroneous operation of the hybrid electric power system.